Current document processing computer systems allow a user to prepare compound documents. A compound document is a document that contains information in various formats. For example, a compound document may contain data in text format, chart format and/or numerical format. FIG. 1A is an example display showing a compound document. The compound document 101 contains text data 102 and 103 and spreadsheet data 104.
FIG. 1B is a block diagram showing a file layout of the compound document shown in FIG. 1A. The file "compound.doc" 111 contains data blocks 112 and 113 containing the text data and data block 114 for storing the spreadsheet data. The data block 114 contains the spreadsheet data in a presentation format 116 and a link 115 to a file 117 that contains the spreadsheet data. A presentation format is a format in which data is easily displayed on an output device. For example, the presentation format may be a bitmap that can be displayed with a standard block transfer operation such as a BitBlt. The file 111 contains the spreadsheet data in presentation format so that the file 117 does not need to be accessed every time the compound document is displayed. The link 115 points to the file 117 where the spreadsheet data is stored in a native format. A native format is a format that is recognizable by the program that created the file.
FIG. 2 shows a method for creating a compound document. A user generates the spreadsheet data 206 using spreadsheet process 205. The spreadsheet process 205, typically under user control, then stores the spreadsheet data 206 in a presentation format (presentation data) and a link (pointer) to the native spreadsheet data in a clipboard 207. The clipboard 207 is an area of storage (disk or memory) that is typically accessible by any process.
Next, the user launches a word processing process 204 to create the compound document 201. The user enters text data 202 and specifies a location in the compound document 201 at which to insert the data in clipboard 207. The word processing process 204 then copies and stores the presentation data and link from the clipboard 207 and displays the spreadsheet data using the copied presentation data in the compound document 201 at the specified location. This insertion process is referred to as "paste linking" from the clipboard. Data that is paste linked into a compound document is referred to as linked data.
A process which stores data in a clipboard is called a source process. A process which copies data from the clipboard is called a consumer process. In the present example, the spreadsheet process 205, which stores data in clipboard 207, is a source process, and word processing process 204 is a consumer process. Typically, a single process acts as both a consumer and source process at different times.
In object-oriented parlance, any collection of data or functions is referred to as an object. Thus, compound document 201, spreadsheet data 206, spreadsheet data 203, and text data 202 are objects. Also, an object that is contained within another object is referred to as a contained object within a container object. Spreadsheet data 203 is a contained object within compound document 201, which is a container object. An object that contains a link to native data is a link object. An object that a link object points to is a link source. In FIG. 2, spreadsheet data 203 is a link object and spreadsheet data 206 is a link source.
Prior systems typically allow a user to establish a connection between a link object and its link source so that modifications to the link source can be reflected when the container object of the link object is displayed. To establish a connection, the user instructs the consumer process to activate the link object. The consumer process activates the link object by starting the source process and establishing a connection with the source process using standard operating system interprocess communication mechanisms in response to user selection. Through this connection, the source process notifies the consumer process when the link source has been modified. The consumer process can then modify its presentation data to reflect the modifications in the link source. Thus, when a connection is established between the link object and its link source, the presentation data in the link object accurately reflects modifications of the link source data.
In certain situations, prior systems allow link source data to be modified without modifying the consumer process presentation data. Thus, the link source data and presentation data can be inconsistent. A user can start the source process, open the link source, and display and modify the link source data. If the user then starts the consumer process, opens the compound document, and displays the presentation data, the displayed presentation data will be inconsistent with the displayed link source data. Since the source process was not started as a result of activating the link object, there is no connection through which consistency can be maintained. This inconsistency is undesirable.